If you are not prompted with a logon screen then you need to check to see if a pop-up blocker is preventing the logon screen.
If you suspect a popup blocker, these instructions may help.
If you are not able to get the logon screen by allowing popups, try this link instead (just don't use the "back" button): Click here to get logon
This site also requires Internet Explorer 7.0 or above, and a minimum screen resolution of 800 by 600.
If you do not have Internet Explorer you will need to install it to enter the site.